inhibits antigen-mediated Syk, but not Lyn tyrosine kinase activation in mast cells

High affinity IgE receptors (αβγ ₂) mediate the activation of the non-receptor tyrosine kinases Lyn and Syk. Here we show that the antioxidant drug (NAC) inhibits antigen-mediated Syk activation whereas Lyn activation and phosphorylation of β and γ is maintained. Furthermore, NAC inhibits antigen-mediated calcium mobilization and exocytosis in a dose-dependent manner, but does not inhibit ionomycin-induced exocytosis. These data support a model in which the activation of Lyn is responsible for receptor phosphorylation and precedes the activation of Syk. The inhibition of Syk activation by NAC may be relevant to B and T cell antigen receptors, which are also linked to Syk/ZAP70 tyrosine kinases.